The invention relates to an apparatus for the examination of specimen with a beam of charged particles. In particular, this invention relates to a miniaturized column for a charged particle beam device. Furthermore, this invention relates to a deflector for a charged particle beam device.
Charged particle beam devices, such as scanning, transmission or micro-probe apparatuses to quote only a few, are powerful instruments which permit the observation, characterization and modification of heterogeneous organic and inorganic materials and their surfaces. In these instruments, the area to be examined (modified) is irradiated with a charged particle beam, which may be static or swept in a raster across the surface of the specimen. Depending on the specific application, the charged particle beam is more or less focused and the kinetic energy of the particles can vary considerably.
The types of signals produced when the charged particles impinge on a specimen surface include e.g. secondary electrons, backscattered electrons, Auger electrons, characteristic x-rays, and photons of various energies. These signals are obtained from specific emission volumes within the sample and can be used to examine many characteristics of the sample such as composition, surface topography, crystallography, etc.
Lately, attempts have been made to miniaturize charged particle beam devices. Several of these devices could then be grouped together to simultaneously examine or modify larger areas of the specimen or they could be installed in process lines with tight space restrictions. Furthermore, since spherical and chromatic aberrations of particle beam devices scale proportional to their geometrical dimensions, as long as the potential remains constant, miniaturized devices would be able to deliver higher spatial resolution and high beam current in a given spot size.
In general, most of the present charged particle devices are between 0,5 and 1,2 meters high with an average diameter of about 15 cm-40 cm. Distinct from that, developers are aiming at producing beam devices which are smaller than 10 cm with an average diameter of about 4 cm. However, since modem charged particle beam apparatuses are complex technical instruments with sophisticated vacuum systems, alignment mechanism and electronic control units, their geometrical dimensions can not simply be shrinked proportionally, even so this is attempted wherever possible.
For forming of the particle beams in the particle beam columns electromagnetic lenses and electromagnetic multipoles are used. Lenses are axially symmetric electromagnetic fields used for focusing of the beam. Electromagnetic multipoles generate static deflecting fields (deflectors) for correction of the beam path through the electromagnetic lenses and for positioning the beam at the specimen, dynamic deflecting fields used for scanning the beam over the specimen and quadrupole fields (stigmators) used for compensation of the aberrations arising from the deviations of the lenses from the axial symmetry. Each particle beam instrument contains usually at least one multipole for alignment, one multipole for astigmatism correction, one multipole for beam shift at the specimen and one multipole for beam scanning at the specimen. Each multipole usually consists of eight electrodes or coils. This can result in large amount, for example 30 to 40, of independent voltages and currents that have to be supplied to the particle beam column.
In a single standard commercial column the number of the control signals required to operate the device does not present a limiting factor. In miniaturised columns and column arrays, however, the large number of the voltages and currents that have to be supplied to each column presents a major problem. Especially, the complexity of the electrical connections required to control every column in a column array increases the cost of an column array significantly. Furthermore, the complexity of the circuits required to control and to drive the large number of the voltages and currents also leads an significant increase of the cost of a column array.
The present invention provides an improved column for a charged particle beam device, especially for miniaturized charged particle beam device. Furthermore, the present invention provides an improved deflector for a charged particle beam device. According to one aspect of the present invention, there is provided a column for a charged particle beam device as specified in independent claim 1. According to a further aspect of the present invention there is provided a deflector for a charged particle beam device as specified in independent claims 17 and 19. Further advantageous, features, aspects and details of the invention are evident from the dependent claims, the description and the accompanying drawings. The claims are intended to be understood as a first non-limiting approach of defining the invention in general terms.
The present invention provides an improved column for a charged particle beam device. The column comprises deflectors for scanning the beam over the specimen, for aligning the beam with regard to the objective and for compensating aberrations caused by the objective. Thereby, the total number of electrode arrangements and/or coil arrangements that are used for the deflectors and that are independently controllable, is 8 or less. This results in a reduction of 50% in the number of signals, that have to be supplied to column in order to control the direction of the beam, compared to the best column known to the inventor. Accordingly, the complexity of the wiring needed to supply these signals the column is reduced considerably. Furthermore, the complexity of the driving circuits is also reduced.
According to a further aspect of the present invention, a deflector for a charged particle beam device is provided. The deflector, according to one embodiment, comprises four electrode arrangements wherein each electrode arrangement consists of three single electrodes, each electrode having the shape of a ring segment, and wherein the four electrode arrangements are positioned along a ring in a manner that between each pair of electrodes from one electrode arrangement an electrode from another electrode arrangement is located. The deflector, according to a further embodiment, comprises four coils wherein two coils are positioned along a first ring and two coils are positioned along a second ring, which is concentric with the first ring and has a larger diameter than the first ring, in a manner that when viewed from the center of the rings every coil positioned on the first ring overlaps with the two coils positioned on the second ring. These improved deflectors have the advantage that they provide a high degree of homogeneity in the electric, magnetic deflecting field, respectively.